Examiner Handbook to the U.S. Patent Classification System

Chapter One: Organization of Information

(found at http://www.uspto.gov/patents/resources/classification/handbook/index.jsp)

Chapter Table of Contents

   * Bases of Classification

   * Search System Organization


A. Bases of Classification

A variety of rationales have been developed over the years to subdivide our classification files into searchable units. Collections of art based on each of the following rationales can be found in the system as it exists today. Thus, keep in mind the strengths and weaknesses of each rationale when conducting a search.

1. Industry or Use

This approach divides art on the basis of the industry employing the art or the use to which a device is put. It provides a unique collection wherein all relevant devices for a given technology are housed in one convenient location. Several original classes were created using this rationale and a number of these classes still exist today, e.g., Bee Culture, Butchering, etc.

A drawback of classifying in the above manner is that physically similar art is separated without a meaningful distinction. Thus, the search process is lengthened. If the above classification process is used excessively, there is a greater chance of issuing two patents for the same idea. To illustrate, the 1872 classification system separated cooling devices on the basis of the product treated in these devices; e.g., beer or milk. These cooling devices could well be analogous and both should be considered in performing any search for cooling devices, per se.

2. Proximate Function

To avoid fragmenting the art based on its industry or use, the U.S. Patent and Trademark Office uses the fundamental, direct, or necessary function as the principal basis of classification. Also, for brevity, the term “proximate” is substituted for the words fundamental, direct, or necessary. Therefore, “proximate” function means that similar processes or structures that achieve similar results by the application of similar natural laws to similar substances are considered to have the same fundamental utility and are grouped together. Our current system provides a single collecting area for all heat exchange devices; e.g., milk coolers, beer coolers, etc. Once collected into this single area, the art is further subdivided on features essential to heat exchange devices.

The term “utility” refers to (1) the function that a process, structure, or composition can perform; (2) the effect of a process, structure, or composition; or (3) the product that is produced by a process, structure, or composition. The proximate function, when used as a basis for classification, is generally applied to a process, structure, or composition for performing general operations in which a single causative characteristic can be identified and which requires essentially a single unitary act; e.g., agitating, cutting, heating, filtering, etc.


3. Effect or Product

This rationale collects art into industrial or trade groupings based on the result produced by the art. This result may be tangible (e.g., the product of a manufacturing process) or intangible (e.g., the communication of sound at a distance). In the mechanical and electrical fields, this method of grouping is generally reserved for complex processes or structures requiring successive manipulations involving plural acts; e.g., telephone system, shoemaking machine, etc. In the chemical fields, processes involving chemical reactions often are classified on the basis of the product produced.

4. Structure

Simple subject matter having no apparent functional characteristics is classified based on the structural configuration or physical makeup of the object. This situation rarely arises with respect to the creation of a large group or class in mechanical fields, but frequently occurs with respect to subdivisions within such group or class.

A chemical compound is always classified on the basis of structure, and a stock material is often classified on the basis of structure. The chemical structure of compounds and the components and arrangement of the components of a stock material determine their classification, irrespective of the utility or utilities involved.

Since the properties of mixtures, or compositions, are not predictable to the same degree as are the properties of chemical compounds, utility is usually the primary basis for classification of mixtures. In the case of certain mixtures, however, such as colloids and alloys, the best classification seems to be on the basis of the components per se.


B. Search System Organization

The following description is a brief overview of the USPC system. This description will acquaint you with terms and phrases used in the handbook. Many of these terms and phrases are explained in greater detail later in this handbook.

A fundamental principle of the USPC system is that each class, or part thereof, was created by:

  1. analyzing the claimed disclosures of the U.S. patents ,

  2. creating various divisions and subdivisions on the basis of that analysis rather than by making a theoretical arrangement or ordering, and, finally ,

  3. classifying the patent documents into the arrangement .

In the USPC system, similar subject matter has been gathered in large groupings to create classes. Each class was then subdivided into smaller searchable units called subclasses. The sequence or pattern arrangement of the subclasses within each class is indicated by the Class Schedule.

Each class and its subclasses, with the exception of alpha subclasses of the utility classes and some of the design classes, have a title and a definition. The title and definition of any subclass in a class schedule are further restricted (a) by the title and definition of the class and (b) by the title and definition of any subclass or subclasses under which they are indented.

The bulk of patent documents stored in the USPC system are U.S. patents. These documents are designated as either “OR” (Original) or “XR” (Cross-Reference) placements. The USPTO began publishing U.S. patent applications in March of 2001, and they too are stored in the USPC. These documents, referred to as PGPub documents as they are “Pre-Grant-Publications”, have a mandatory classification called a “Primary” classification and may additionally include “Secondary” classifications.

The OR classification is based on the claims in the patent. It is a mandatory classification assigned to a patent that has the same class as the class of the controlling claim. Only patents designated as Originals in a subclass are used, in conjunction with the definition of the subclass, to define the “body of art” encompassed by the subclass for the purpose of determining where newly filed applications are best assigned for examination.

A Cross-Reference placement is an additional classification added to a patent to a different sub­class in the system. Refer to Section V and Section VI in this handbook for more information on this subject.

Every PGPub document must have one, and only one “Primary” classification. The Primary classification for a PGPub document is representative of the main inventive concept within the complete disclosure, using the claims as a guide.

PGPub documents may also be assigned “Secondary” classifications based on invention information, or other information considered to be valuable for search. Assignment of secondary classifications based on invention information is mandatory, while Secondary classifications based on non-inventive, but otherwise valuable, information are discretionary.

The USPC system also contains many foreign patent documents and non-patent literature references. The procedure for classifying foreign patent documents and non-patent literature in the system is simpler than the procedure for classifying U.S. patent documents. Total disclosure is generally used in classifying foreign patent documents and non-patent literature.

Until October 1, 1995, the U.S. Patent and Trademark Office received copies of foreign patent documents from other countries and classified them into the USPC system. Beginning in October 1995, however, newly published foreign patent documents were no longer classified into the USPC system. USPTO now receives most foreign patents on CD-ROM disks. These foreign patents on CD-ROM are accessible from the Foreign Patents Branch of the Scientific and Technical Information Center, through the Foreign Patents Access System (FPAS).

Also, after October 1, 1995, copies of foreign documents in the examiner files were no longer automatically reclassified during a USPC reclassification project. In some cases, the foreign documents associated with a reclassification project remain in the old US classifications, which are transformed into “Foreign Patent Art Collections.” These collections appear at the end of the class that includes the newly created U.S. subclasses. Foreign Patent Art Collections are identified by their subclass numbers, which include the prefix “FOR,” followed by a 3-digit number.

Each Foreign Patent Art Collection contains, in parentheses at the end of the title, the subclass number in which the foreign patent documents were classified before the reclassification project.

Subclass definitions are maintained for the Foreign Patent Art Collections that exactly correspond to those of the former classification schedule.

Some foreign patents continue to be filed in the examiner search files by IPC class. See attachment B to Section IV of the Manual of Classification for a listing.

E-subclasses are USPC subclasses that are equivalent in scope to classifications in the European Classification system, ECLA, on a one-to-one basis. These subclasses appear at the end of the USPC class schedules in which they exist (at the time of this writing, they exist only in class 257) and can be identified by their subclass numbers, which begin with the letter “E”.

E-subclasses represent a transitional harmonization effort by the USPTO to begin using ECLA classifications. The definitions of E-subclasses state which ECLA classification the E-subclass corresponds to. It may or may not provide a detailed description of the metes and bounds of the art encompassed by the subclass.


The documents classified in E-subclasses should be reviewed to determine the subject matter encompassed by an E-subclass whenever the scope of the subclass cannot be determined from the title or its definition.

E-subclasses are similar to cross-reference art collections in that they cannot take original placements of U.S. patents or Primary classifications of PGPub documents.

At the time of their creation, E-subclasses are populated with documents from their equivalent ECLA classifications. Subsequently, U.S. patent documents are classified and maintained in E-subclasses by USPTO, while the classification and maintenance of non-JP foreign documents is performed by EPO. Foreign documents are regularly placed in the E-subclasses through the DOCDB data supplied to USPTO by the EPO.

An E-subclass title ending with the expression “(EPO)” indicates that documents classified by the EPO have been and are regularly placed in the subclass. An E-subclass title may also include a “(JPO)” suffix which indicates the subclass has JP documents placed by the JPO. This would typically be done for E-subclasses corresponding to IPC level classifications. Even though an E-subclass may not have documents placed by JPO, it should be remembered that EPO has placed many JP documents into ECLA that are classified in the E-subclasses.

In rare instances, an E-subclass may have no “(EPO)” or “(JPO)” suffix on its title. This indicates the subclass was created solely by USPTO and that there is no equivalent ECLA classification. These E-subclasses are not regularly populated with foreign art from the EPO or JPO. In order to review foreign patent documents pertinent to the subject matter provided for by these E-subclasses, one must review the documents classified in the parent subclass that does provide for them.

When an examiner or classifier places a mandatory classification for a U.S. document in a subclass whose title begins with a parenthesized “(E)”, at least one cross-reference classification is normally assigned to an E-subclass at the end of the class schedule. Mandatory classification include OR and Primary classifications, as well as any mandatory XR and Secondary classifications.

Specific search tools are used to access information contained in the system. The following discussion provides detailed information on these tools and how to use them.


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